Muffler - Backfiring.

[Morcs]

Ive been using a straight through can on my nc35 for a while now, and its always run pretty sweet.

When a low profile is necessary I change back to the standard one.

But ever since ive put new plugs in the aftermarket one backfires heaps ( I mean HEAPS) the slightest back-off of the throttle at any rpm and it pops and crackles away.

firstly, is it damaging my valves or anything like that?
secondly, how is this caused? I wouldve thought nice shiny new plugs would get a better burn and leave less fuel to ignite in the exhaust.

Its a 3 bolt that ive been sealing with greymax. Maybe im not sealing enough or too well?

Please advise. Im back on the standard one for now, and I hate my bike sounding so shit.

[xwhatsit]

When trying to make my bike idle when hot, I experimented by doing two things -- changed the ignition lead, and closed up the gap on the plug. Neither fixed my problem, but I had way more popping and crackling on the over-run (and not just from high rpm either), and at part throttle. Going back to a normal (new) plug and the old lead fixed it.

Never bothered to work out which was the cause, but both leads are identical so I'm guessing it was the smaller gap on the plug. Are they the same plugs? Have you set the gap correctly? I always set the gap when I buy a new plug -- often it's different, despite buying the same model plug dozens (no, really) of times. Set it to what's in the manual.

[huck farley]

Me thinks you are running to lean, also the backfire is caused by a leak in the exhaust system. What causes most bikes to backfire is that there is no back pressure, and what's happening the exhaust is sucking in the air on deceleration and it mixes with the spent gases and creates an explosion, and that's where all the snap crackle and pop is coming from. I personally don't think that changing the plugs should cause it. Well that's my two penneth worth. Some one may have a better theory.

[heyjoe]

Ive been using a straight through can on my nc35 for a while now, and its always run pretty sweet.

When a low profile is necessary I change back to the standard one.

But ever since ive put new plugs in the aftermarket one backfires heaps ( I mean HEAPS) the slightest back-off of the throttle at any rpm and it pops and crackles away.

firstly, is it damaging my valves or anything like that?
secondly, how is this caused? I wouldve thought nice shiny new plugs would get a better burn and leave less fuel to ignite in the exhaust.

Its a 3 bolt that ive been sealing with greymax. Maybe im not sealing enough or too well?

Please advise. Im back on the standard one for now, and I hate my bike sounding so shit.

Hi there morcs,

I am not familiar with your bike or its exhaust but from my experience I suspect that you may have a leak in your exhaust system somewhere where air is getting in and causing the backfiring (loud popping). This popping is usually air mixing with spent exhaust gasses and igniting in the exhaust causing a small explosion in your cans. It usually happens on deceleration. Cause of air getting in may be improper/ poor seal at the exhaust gasket area where your header pipe connnects with the exhaust manifold. It only takes the slightest poor seal to allow air to be sucked in. Changing pipes sometimes damages exhaust manifold gaskets or spoils the nice seal they did have ex factory and when you re-use them again - they are never quite the same. New ones will fix that and they don't cost too much so just get new ones. I don't think its your plugs and I don't think your valves will come to harm as the gas burning is occuring in your exhaust not in the engine. I am not familiar with greymax or your bike as I said but my comments coupled with what huck farley says (see below) I think might help with some possible answers. Also check the tightness of the bolts holding the headers onto the exhaust manifold to ensure they are torqued correctly to manufacturers specs.

Me thinks you are running to lean, also the backfire is caused by a leak in the exhaust system. What causes most bikes to backfire is that there is no back pressure, and what's happening the exhaust is sucking in the air on deceleration and it mixes with the spent gases and creates an explosion, and that's where all the snap crackle and pop is coming from. I personally don't think that changing the plugs should cause it. Well that's my two penneth worth. Some one may have a better theory.

I agree that pipes do need back pressure and if your replacement ones are literally straight through then you may find it running rough or lack power (sound sick). Perhaps modifying the new ones to build in some back pressure will help.

I am not an expert nor a mechanic. I hope this gives you some ideas though. Good luck in finding a solution.

[Morcs]

When trying to make my bike idle when hot, I experimented by doing two things -- changed the ignition lead, and closed up the gap on the plug. Neither fixed my problem, but I had way more popping and crackling on the over-run (and not just from high rpm either), and at part throttle. Going back to a normal (new) plug and the old lead fixed it.

Never bothered to work out which was the cause, but both leads are identical so I'm guessing it was the smaller gap on the plug. Are they the same plugs? Have you set the gap correctly? I always set the gap when I buy a new plug -- often it's different, despite buying the same model plug dozens (no, really) of times. Set it to what's in the manual.

Im pretty sure its the plugs. you just triggered my memory so I went and checked.

I bought the correct plug listed for the bike - NGK ER9EH, but the ones I took out are ER8EH...

According to my research:

Spark plug (standard) NGK ER9EH
Spark plug (racing) NGK ER10EH
Spark plug (cold climate) NGK ER8EH

Anyways, I know I have a leak. Its at the linkage where the back 2 cylinders' pipes join the front. Im pretty sure as shops keep using it as a jack-up point

[westie]

My post was moved to detention. So I can not offer the assistance you need.
Sorry

[Morcs]

My post was moved to detention. So I can not offer the assistance you need.
Sorry

Eh?

you werent offering ass-istance again were you?

[Kickaha]

My post was moved to detention. So I can not offer the assistance you need.
Sorry

I don't consider the phrase "stop riding like a fag" assistance


This is a technical forum only so no drivel will be tolerated.

Do not complain if you find your posts deleted unless you believe it had technical value.

[limbimtimwim]

How many KM on the clock?

Mine was a little poppy before I got the valve shims done.

[xwhatsit]

Those plugs should be fine, though; that number is just the heat rating. Unless they're getting super hot and giving up the ghost or something silly, which sounds odd.

Fix your exhaust leak -- if nothing changes, then it's time for head scratching.

[klyong82]

According to my research:

Spark plug (standard) NGK ER9EH
Spark plug (racing) NGK ER10EH
Spark plug (cold climate) NGK ER8EH

The CR9EH9 plugs are cooler plugs (suitable for cooler climate riding) than the CR8EH9. I think the VFR/RVF standard plugs were CR9EH9.

[fireball]

my bike is very poppy and backfiring due to a leak/blown head gasket have you had a close look at your header pipes? even the smallest gap will cause a problem...

[limbimtimwim]

I think the VFR/RVF standard plugs were CR9EH9.

Nah, the RVF uses the infamous (To me anyway) NGK ER9EH or ER10EH or Nippon Denso Y27FER or Y31FER Or.. if you are insane, the ND IY27 iridium plug.

Maybe next year as a present if it behaves itself. But only if it's good.

[Morcs]

Nah, the RVF uses the infamous (To me anyway) NGK ER9EH or ER10EH or Nippon Denso Y27FER or Y31FER Or.. if you are insane, the ND IY27 iridium plug.

Maybe next year as a present if it behaves itself. But only if it's good.

I was running 8s. changed to 9s. It hurt. $45 per plug

Hurry up and try the iridiums and tell me how they go

Thats if i can be bothered spending another 2 hours changing the buggers...

[limbimtimwim]

Horrendous isn't it? The local importer isn't being fair.

Tyga sell them for less each, I don't know if you'd end up winning once you paid shipping.

I'm not really going to try the Iridium ones, I can't imagine how many units of blood I'd have to sell to pay for those.